1. Field of the Invention
The present invention relates to an etching method and particularly to an etching method applicable to the case that a cavity portion to form is larger than a size of an etching opening or the case that a cavity portion having a complicated structure is formed when a microstructure having a cavity portion is formed in production of a semiconductor apparatus or a micromachine.
2. Related Art
With development of microstructure technologies, micromachines (Micro Electro Mechanical Systems: MEMS) and small devices including a micromachine have attracted attention. The micromachine is an element in which a movable portion comprising a three-dimensional structure formed on a substrate, such as a silicon substrate and a glass substrate, and a semiconductor integrated circuit or the like for control of driving the movable portion are electrically, mechanically combined.
Conventionally, as a technology for providing the three dimensional structure, in such a micromachine field, a three-dimensional structure having a cavity portion under a patterned structure layer is provided by previously forming a sacrifice layer on a substrate, forming a structural member layer on this sacrifice layer which is patterned, and then selectively removing the sacrifice layer. As the sacrifice layer, silicon dioxide (SiO2) or silicon (Si) is used.
If the sacrifice layer is formed with silicon dioxide, an etching liquid of Fluorine (F) type is used as an etchant and if the sacrifice layer is formed with silicon, an etching gas such as Xenon fluoride (XeF2), and bromine fluoride (BrF3) is used as an etchant, for example in Japanese laid-open patent application No. 2002-214548, particularly paragraphs 0002 and 0030.
For example, if a three-dimensional structure is formed having a structure as shown in FIG. 1, first, a sacrifice layer 2 is buried in a hollow portion 1a formed on the surface side of the substrate 1 and a structural member layer 3 is formed to cover the substrate 1 and the sacrifice layer 2. Next, the structural member layer 3 is patterned to have a required configuration as well as an etching opening 3a reachable the sacrifice layer 2 is formed in the structural member layer 3. After that, the sacrifice layer 2 is removed by etching through the etching opening 3a. This forms a cavity portion “a” under the structural member layer 3. This forms a cavity portion “a” under the structural member layer 3. Here in this etching, as described above, a suitable etchant is selected in accordance with the material forming the sacrifice layer.